Field of the Invention
The present invention relates to an image forming apparatus, a method of controlling the same and a storage medium.
Description of the Related Art
Conventionally, the following schemes exist as a print schedule for a case of printing print data in which image data for which double-sided printing is designated and image data for which single-sided printing is designated are mixed.
A first scheme switches double-sided printing and single-sided printing as designated by the print data. In this scheme, when double-sided printing and single-sided printing are switched, the conveyance path of paper is switched to a double-sided paper feed path (a paper feed path for double-sided printing) or a single-sided paper feed path.
In the double-sided printing which uses the double-sided paper feed path, a paper is conveyed to a transfer unit, and an image is printed on one side of the paper. Then, the paper whose one side is printed, is sent to a paper reversing unit to be reversed, the paper passes through the double-sided paper feed path and is once again sent to the transfer unit, and an image is transferred to the side opposite to the side of the paper first printed to, thereby realizing the double-sided printing to the paper. Furthermore, to improve the productivity by filling the interval between papers, when performing double-sided printing consecutively, rather than performing transfer to the first side and transfer to the a second side on the opposite side thereof for every paper, a plurality of papers are fed collectively, and images of the first side of these papers are consecutively printed. After this, the plurality of papers on the first sides of which an image is printed are sent to the double-sided paper feed path; a double-sided circulating control is performed wherein printing of an image of the first side of papers that are newly fed, and printing of an image on the second side of the papers conveyed via the double-sided paper feed path are alternatingly executed. By doing this, it is possible to print without interval between papers occurring in a case where double-sided printing is consecutive, which is therefore is efficient. However, if single-sided printing and double-sided printing are switched frequently, productivity is lowered because intervals between papers in the double-sided paper feed path are generated.
A second scheme solves this problem. In the second scheme, in order to reduce a lowering of productivity due to intervals between papers, printing is performed by causing papers for which only one side is printed to pass through the same conveyance path as the papers for which both sides are printed (for example, refer to Japanese Patent Laid-Open No. 2010-105350). In the second scheme, if an image for which single-sided printing is designated is printed during execution of double-sided printings, the image data corresponding to the back side of the image for which the single-sided printing is designated is converted to image data to be printed as blank sheet image data, and the paper is caused to pass through the double-sided paper feed path. With this, it is possible to print consecutively without generating intervals between papers.
In the foregoing conventional image forming apparatuses, there are cases that occur in which the generation of the subsequent image data does not keep up for the cycle of the double-sided circulating control due to time being required for print data analysis processing. Also, in cases where printing is temporarily interrupted by a paper jam or a paper outage, the cycle of the double-sided circulating control stops. When the reason for the stoppage is cancelled, and printing is restarted, the control to cause a paper on which head image data is to be printed to pass through the double-sided paper feed path is performed even in cases where the head image data is image data for which single-sided printing is designated. Accordingly, there is a problem in that the head image data is single-sided printing, and compared to a case in which the head image data is single-sided printed, productivity is lowered. Furthermore, by the foregoing conventional technique, there is a problem in that a paper of the single-sided printing is caused to pass through the double-sided paper feed path unnecessarily for printing the paper, and the consumption of parts of the conveying path is accelerated.